Film shrinking tunnel utilizing hot air and water as heat transfer medium

ABSTRACT

An apparatus for shrinking the film around packaged food products such as meats, cheeses and the like, which utilizes a combination of hot oven air and water as a heat transfer medium to the packaged food products by completely surrounding the products with a hot wet mist cloud, at a carefully controlled temperature, so as to produce an ideal condition for effecting a shrink rate near the maximum capability of the film and best suited for individual products.

United States Patent Worline [4 1 July 18, 1972 [54] FILM SHRINKING TUNNEL UTILIZING HOT AIR AND WATER AS HEAT TRANSFER MEDIUM [72] Inventor: Paul W. Worline, 125 Midway Road, Oak

Ridge, Tenn. 37830 [22] Filed: June 18, 1971 [21] Appl. No.: 154,412

Related US. Application Data [63] Continuation-impart of Ser. No. 24,499, April 1,

1970, abandoned.

52 us. (:1. ..219/388, 53/184, 99/443 c, 107/57 B, 219/401 51 1111. C1 ..F27b 9/06, F27d 1 1/02 58 Field of Search ..219/388, 401; 99/386, 443 c;

[56] References Cited UNITED STATES PATENTS 1,771,020 7/1930 Thurm et al ..107/S7 B 2,880,522 7/ 1957 Rollings ..99/443 C 3,222,800 12/ 1965 Siegel et 31.... ..34/2l2 3,272,154 9/1966 Kratz ....219/388 X 3,312,811 4/1967 Shanklin ..219/388 3,320,945 5/1967 Dunkelmam. ....2l9/401 X 3,378,989 4/1968 Denker ..53/ l 84 3,389,535 6/1968 Armetti ..53/1 84 3,399,506 9/ 1968 Howe, .lr... ..53/39 Primary Exanfiner-Volodymyr Y. Mayewsky Anamey-John W. Melville et a1.

[57] ABSTRACT An apparatus for shrinking the film around packaged food products such as meats, cheeses and the like, which utilizes a combination of hot oven air and water as a heat transfer medium to the packaged food products by completely surrounding the products with a hot wet mist cloud, at a carefully controlled temperature, so as to produce an ideal condition for effecting a shrink rate near the maximum capability of the film and best suited for individual products.

11 Chlns,6Drawingflgures PmNIEnJuuamz 3,678,244

ATTORNEYS FILMSHIUNKINGTUNNELUHIJZINGHOTAIRAND WATER AS HEAT TRANSFERMHXUNI CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of Application Ser. No. 24,499, filed Apr. 1, 1970, now abandoned, in the name of PAUL W. WORLINE.

BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to the pre-packaging of food products, such as fresh and smoked meats, cheeses and the like, and, more particularly, to an apparatus for pre-packaging food products using a heat-shrink film forming the outer wrapping thereof.

2. Description of the Prior Art The trend in supermarket marketing of food products, such as fresh and smoked meats, cheeses and the like, has long been prepackaging. For example, fresh and smoked meats have been wrapped in the supermarket for some time with heat shrinkable materials, such as regular type Saran film, and then put onto the counter for display and sale. While these heat shrinkable materials generally provide an inexpensive, substantially airtight package which will prevent contamination of the product when properly heat sealed and which will maintain'most perishable items in a state of freshness for a relatively long period of time, the packaging of fresh or smoked meats in this manner has generally been unsatisfactory, because the meats do not have a long shelf life, i.e., the meats do not retain a freshly cut and packaged look. This is so, for example, because red meats start to discolor quickly and turn to a darker hue, and smoked meats, including ham, lose their fresh pink color and turn dull and faded out. Such appearance is obviously very unattractive to the consumer.

It has generally been found that the aforementioned discoloration of meats on the supermarket counter is due primarily to the bacteria which have been sealed into the package and which come into contact with the air inside the wrapping, Due to the fact that most bacteria thrive when exposed to air and that few micro-organisms can survive in an atmosphere void of air, the necessity of vacuum packing the food products in some sort of Saran or polyethylen package, whereby all the outside air is eliminated from the package and the package securely sealed at the same time, has been demonstrated. However, this type. of packaging does not present the best appearance because the plastic bag or pouch into which the product is put is larger than the product itself. Accordingly, when the bag or pouch is vacuumized it creates a very wrinkled and unattractive package. I

A further solution to the pre-packaging problem has been sought by the various attempts to successfully utilize shrinkable film. Here the product may easily be placed into a larger shrinkable film bag or pouch, and the bag or pouch completely evacuated by vacuum so that the film is then shrunk and exactly fits the product without wrinkles. Exemplary shrinkable films now on the market are Saran S and Polyethylene P, both having a shrink capacity of approximately 40 percent.

Numerous systems have been utilized in an attempt to successfully shrink the film around packaged food products. Such systems have included the use of hot air (see for example, United States Letters Pat. Nos. 3,349,502; 3,399,506; and 3,309,835), infrared heat,,and submersion of the products in hot water. However, all of these systems have left much to be desired. For example, the use of hot air has been found to be entirely unacceptable, and the use of infrared heat has also proven to be unacceptable because of the spotty coverage that results, i.e., places on the top, sides and bottom of the packages that are not touched by the heat because the spots where the film is in direct contact with the meat will require a different degree of heat for shrinkage than the area which has a void underneath and is not in contact with the meat. The real problem with all hot water systems now in use is that the shrinkable film is very sensitive to over-heating and such hot water systerrs do not subject the product to a temperature sufficient to shrink the film to its maximum without overdue exposure of the product itself to excessively high degrees of temperature.

Exemplary of a water system which is probably the most successful water system presently in use, is the system which utilizes hot water from a water heater. The water is pumped into a tank over the conveyor which takes the packaged food products through an oven, and a curtain of water, caused by the flow of gravity, flows down over the packaged food products as they pass thereunder. While the reaction of the film to this particular hot water system under ideal conditions is very fast and almost instantaneous, and it is possible to shrink most types of film substantially their full 40 percent in a matter of seconds, this particular system has proven unsatisfactory because it is extremely difiicult to maintain a water temperature close to the ideal conditions. Additionally, such a system generally utilizes a sump in the bottom thereof to hold the supply of water and to catch the water as it is spilled over the packaged food products. The wateris then recirculated through the heater and then returned to the weir box and again discharged onto the products on the conveyor. An unsanitary condition is obviously created because the water is continually used over and over again.

In order to use the aforementioned water system with complete sanitation assurance, it would be necessary to completely change the water in the sump at frequent periodic intervals. This would, of course, be very expensive from the operational standpoint.

In summary, the aforementioned hot water system is unsatisfactory because the proper temperature of the heat transfer medium, which is water, cannot be maintained exact enough and long enough to successfully shrink the film to its full extent. Additionally, the system presents certain definite unsanitary conditions. I

Still another hot water system has attempted to obtain film shrinkage through the complete submersion of packaged products in hot water. However, the timing necessary for the complete submersion of the product is so critical that this system does not obtain complete shrinkage of the film without overdo exposure of the product to high degrees of temperature.

Accordingly, it is an object of the present invention to develop an apparatus for shrinking the film around packaged food products, such as meats, cheeses and the like, which will subject the product to a temperature sufiicient to shrink the film substantially to its maximum without overdue exposure of the product itself to excessively high degrees of temperature.

It is still a further object of the present invention to provide an apparatus for shrinking the film around packaged food products which will pass the heat transfer medium through the system once, after which time it will not be recirculated but will be exhausted therefrom and drained out.

It is a further object of the present invention to provide an apparatus for shrinking the film around packaged food products which will utilize a substantially smaller amount of heat transfer medium than has heretofore been used by prior art devices.

SUMMARY OF THE INVENTION The present invention provides an apparatus for shrinking the film around packaged food products which is a combination of the aforementioned hot air process and the use of the supporting means and the heating means and a plurality of atomizing nozzles are positioned in the oven above the supporting means, each of the nonles being operatively connected to a source of hot water, the temperature of which is carefully controlled within the range of about 190 F. to 210 F. and being capable of producing a full cone of water vapor.

In operation, the packaged food products in the oven are completely surrounded with a wet mist cloud under a carefully controlled temperature so as to produce an ideal condition for effecting a shrink rate near the maximum capability of the film. Since there is a control on both the hot air and the hot water, the apparatus of the present invention ofiers extremely close control of the ideal temperature for shrinking the film around a variety of packaged products, and the cycle or exposure time, i.e., the time that it takes a product to completely pass through the oven, may be reduced so that it is considerably shorter-than the cycle or exposure time for an oven having less desirable characteristics. It will, of course, be evident that if thecycle or exposure time is shorter, less heat is induced into the packaged food products, and better packaged products are obtained.

The apparatus of the present invention does not recirculate the water over and over again. The water is used once, passes through the system once, and is then exhausted as steam or drained out. Additionally, it should be noted that a stream of water is not injected into the oven. Instead, the apparatus is injecting a very small amount of water which has been completely atomized into very small particles. Accordingly, the apparatus of the present invention will consume substantially less water than prior art devices.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view, partially broken away, of the apparatus of the present invention for shrinking the film around packaged food products.

FIG. 2 is a side elevation of the apparatus of FIG. 1.

FIG. 3 is an end elevation of the apparatus of FIG. 1 as seen from the entrance end.

FIG. 4 is a plan view of the apparatus of FIG. 1.

FIG. 5 is an electrical schematic diagram of the apparatus of FIG. 1.

FIG. 6 is an enlarged front elevation of the central panel of the apparatus of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning first to FIGS. 1 through 4 of the drawings, it will be seen that the shrink tunnel 10 of the present invention for shrinking film around packaged food products, such as the prevacuumized package P, which may comprise a base element or tray T having the product M disposed therein wrapped in heat-shrinkable film P having a peripheral seal or weld S generally extending about the entire periphery of the package, or the prevacuumized product M wrapped in the heat-shrinkable film F having a retaining ring closure R, includes a frame 11 supporting an oven 12 having enclosing insulated walls 12a which provide at least one opening 14 for the passage of packaged food products. In a preferred embodiment, the enclosing insulated walls 12a of the oven 12 will define a tunnel the end walls 12b of which are provided with oppositely spaced openings 14 for the ingress and egress of the packaged food products.

The supporting frame 11 is constructed with stainless steel tubing, and is continuously heliarc welded with no penetrations into or through the tubing. The enclosing walls 12a of the oven 12 of the tunnel 10 are of double wall-fully insulated heliarc welded all stainless steel construction. Additionally, full doors 16 are provided on each end of the tunnel 10 which are hinged with quick-snap latches and which swing open to expose the entire inner tunnel for cleaning and sanitizing. Three inspection doors 18 are provided in the lower section 38 of the tunnel 10.

Free swinging curtains 20, preferably of silicon coated fiberglass, are attached to each end 12b of the tunnel I0 so as to cover the openings 14 and prevent excess vapor spillout.

A gravity-fed roller conveyor assembly 22 carries the prevacuumized, enclosed product onto an endless, motor driven, foraminous, flexible, belt, such as the grid or rod belt 24, positioned within the oven 12. The flexible grid or rod belt 24 is positioned on a conveyor guide rod assembly 26, and a conveyor drive sprocket assembly 28, including the sprockets 30, a roller chain 32 and a variable speed motor 34, control the movement of the grid or rod belt 24, and thus the movement of the film enclosed products through the tunnel 10. In operation, the grid or rod belt 24 preferably travels at a fixed speed that allows approximately three or four seconds exposure time for the film enclosed product.

A vaporizer pan 36 is mounted, as be welding or the like, within the section 38 of the tunnel 10 beneath that portion of the grid or rod belt 24 which carries the film wrapped product. The rails 37 with the edges of the pan 36 support the belt 24. The pan 36 is provided with drain slots 40 leading to a drain 42 in the lower section 38, which, as will be more fully explained hereinafter, precludes the accumulation of excess water in the pan 36, as if excess water is allowed to accumulate in the pan 36, the carefully controlled temperature within the oven will be affected, resulting in poor shrinkage of the product film.

Pan heaters 44, which are preferably of the U-type, are mounted in the section 38 of the tunnel l0 beneath the vaporizer pan 36. In practice, it has been found that nine 1.35 kilowatt pan heaters are satisfactory. Additionally, air convection heaters 46, which are also preferably of the U-type, are mounted in the section 38 beneath the pan heaters 42. In prac tice, it has been found that nine [.35 kilowatt convection heaters are satisfactory. It may also be desirable to include additional auxiliary pan heaters, such as the heaters 44a, 44b and 44c shown in FIG. 5, in the lower section 38, as desired.

The wiring for the heaters 44' and 46 is carried through the heater wiring troughs 48 to the control panel or electrical cabinet 50. As can be seen from FIGS. 5 and 6, which show the electrical schematic diagram and the electrical cabinet details, respectively, the nine pan heaters 44 are switch controlled from the terminal blocks 52 of the control panel 50. Any auxiliary pan heaters 44, such as the heaters 44a, 44b and 44c, shown in FIG. 5, as well as at least three of the air convection heaters 46, such as the air convection heaters 46c, 46h and 461', are connected to a percentage timer or percentage input controller 54 located in the control box. Additional air convection heaters 46, such as the heaters 46c, 46d and 46f, are controlled by an indicating thermostat 56, a first pointer of which indicates the temperature within the oven 12 and a second pointer of which may be set at a desired temperature. The indicating thermostat 56 is electrically connected to the thermostat bulb 57 located in a wall 12a of the oven 12.

It will, of course, be obvious that the entire electrical system will be watertight.

A plurality of atomizing noules 58 are positioned in the oven 12 of the tunnel 10 over the grid or rod belt 24. Each of the nozzles 58 is operatively connected to a source of heated water and is capable of producing a full zone or cone of water vapor 60 in the oven 12 of the shrink tunnel 10.

Water from any suitable outside source is directed to the inlet pipe 62, where the pressure thereof is regulated by the pressure regulator 64 and the flow to the water heater 66, and thus to the atomizing noules 58, is controlled by the solenoid valve 68. It should be noted that when the water heater switch is on, the solenoid valve 68 will open and water will start spraying through the noales 58 into the oven 12 of the shrink tunnel 10.

A line strainer 70 as well as a dial thermometer 72 are preferably disposed in the line between the nozzles 58 and the water heater 66. Additionally, a water thermostat 74 is located adjacent the water heater 66.

After the shrink tunnel has been situated in the proper installation area, it should be leveled to the proper height. This may be accomplished by utilizing the leveling feet 76. The infeed gravity roller assembly or conveyor 22 should preferably be a minimum of two inches higher than the grid or rod belt 24. Additionally, the height of the tunnel 10 should be such that the infeed end will be one-half inch lower than the exit end. This will allow all the excess water to drain through the slots 40 in the vaporizer pan 36, as the shrink tunnel will not perform properly if water is allowed to accumulate in the vaporizer pan 36.

The water inlet 62 should be connected to a source of water. Additionally, the electrical service should be connected to the control panel 50. The exhaust outlets 78 on each end of the tunnel 10 should be connected to a suitable exhaust stack, which in some cases may require a vent fan or blower.

The drain 42 from the bottom of the tunnel should be connected to a water drain.

Operation of the shrink tunnel 10 is initiated by opening the valve (not shown) which controls the water supply to the inlet pipe 62. The switch for the grid or rod belt 24 should then be turned on, followed by the water heater 66. When the water heater 66 is turned on, the solenoid valve 68 automatically opens and waterwill start spraying as a water vapor cone 60 into the oven 12.

In practice, the water thermostat 74 is pre-setand the water temperature should quickly come up to about 210 F., as indicated by the dial thermometer 72 in the water line. The thermostat 74 should at all times maintain the water temperature within the range of about l90 to 210 F. before atomization in the oven 12.

The pan heaters 46 should then be turned on by actuating their respective switches in the control panel 50. The air or convection heater switches in the control panel 50 are then actuated, at which time the shrink tunnel 10 is in complete operation.

The upper limit of the temperature in the oven 12 of the shrink tunnel 10, which is preferably at least 212 F., is controlled by the indicating thermostat 56, which controls a group of convection heaters, such as the heaters 46c, 46d and 46f. When the first pointer of the indicating thermostat 56, which indicates the temperature of the oven 12, reaches the second pointer, or set mark thereof, the indicating thermostat 56 switches off the group of convection heaters 46 connected thereto and the temperature in the oven 12 begins to fall. After the temperature has dropped a degree or two, these heaters 46 are-switched back on again so that the temperature will remain very close to the set point.

The percentage input controller or percentage timer 54, located in the control panel 50, may then beadjusted upward. This raises the percentage of heat output from the group of heaters 44 and 46 connected to it, such as the auxiliary pan heaters 44a, 44b and 44c, shown in FIG. 5, and the convection heaters 46c, 46h and 46i, as best seen in FIGS. 5 and 6, and will take care of lower than normal temperatures in the oven 12, which may result, for example, from a large number of cold input products. It should, of course, be emphasized that the percentage input controller or percentage timer 54 should not be set higher than is necessary to obtain proper operation of the shrink tunnel l0.

The convection heat in the oven 12 may be properly balanced as follows:

l. The second pointer or set mark of the indicating thermostat 56 should be set to the desired temperature.

2. The percentage input controller or percentage timer 54 should be set to 100 percent.

3. The shrink tunnel 10 should be started up by turning all switches on the control panel 50 to the on position.

4. When the first pointer of the indicating thermostat 56 indicates that the temperature of the oven 12 has reached the set temperature, the second pointer should be reset to a temperature somewhat less so that the heaters 46 controlled thereby will not come on.

5. The percentage input controller or percentage timer 54 should be adjusted to maintain the desired temperature within the oven 12. If the first pointer of the indicating thermostat 54 indicates that the temperature of the oven 12 is still increasing, the percentage setting of the percentage timer or input controller 54 should be reduced until the desired temperature may be maintained.

6. The second pointer of the indicating thermostat 56 may now be returned to the set point or desired temperature. The convection heat should now be balanced so that the desired temperature can be maintained under normal operating conditions, and as the product load increases, the heaters controlled by the indicating therrnostat 56 will come on, maintaining a close temperature control under all operating conditions.

The shrink tunnel 10 may be equipped with either a high temperature warning light 80, which is red in color and located on the cover of the control panel 50, or with a high temperature safety electrical disconnect system 84, which automatically shuts down the shrink tunnel 10 when it is overheated. The warning light is controlled by a thermostat 82 located in a water tight box at the discharge end of the tunnel 10. The thermostat 82 has been preset for 240 F. If the warning light 80 should come on, the tunnel should be shut off completely, as the overheating indicates that the water to the tunnel has been shut off, the solenoid valve 68 controlling the water has malfunctioned, or the atomizing nozzles 58 are plugged or partially blocked.

In operation, as the prevacuumized package P or the prevacuumized product M on the grid or rod belt 24 moves through the oven 12, the temperature within the oven 12 is carefully controlled as herein before described to the temperature best suited for that product and shrinkable film F which is being utilized. Hot water from the water heater 66 is injected in cone fashion 60 into the hot oven 12 through the atomizing nozzles 58, and the atomized water settling in the vaporizer pan 36 is reheated to form a dense hot vapor or steam cloud that will completely surround the product.

The use of a hot water mist injected into the closely controlled temperature of the oven 12 produces the optimum heat transfer medium, which greatly reduces the exposure time of the product in order to obtain full shrink of the film, as compared with the exposure times of systems with less desirable characteristics. Accordingly, substantially less heat is transferred to perishable products. For example, it has been found that it is possible to shrink the film around red meats with a total product exposure to the environment inside the oven 12 of no longer than three seconds. Such the Saran 8" or Polyethylene P" film in itself is a very good insulator, an exposure time this short will induce little heat into the products.

Due to the very small amount of water required by the shrink tunnel 10 of the present invention, which should not exceed 5 or 6 gallons of water per hour, all condensation from hot vapor is discharged, thereby maintaining a completely sanitary heat transfer medium to the product.

The shrink tunnel 10 of the present invention is completely self-contained and needs only one electrical connection to the control panel 50 and one cold water connection to the inlet pipe 62. Additionally, the shrink tunnel 10 of the present invention contains no pumps or other troublesome mechanical devices, and the only moving parts are the roller assembly 22, the grid and rod belt 24, the conveyor guide rod assembly 26 and the conveyor drive sprocket assembly 28.

The shrink tunnel 10 of the present invention provides a substantial savings in time and cost by bringing lower operating cost, faster processing, and the assurance of a high degree of sanitation.

It should, perhaps, also be noted that the shrink tunnel 10 of the present invention is constructed such that the highest degree of sanitation may be maintained.

While certain preferred embodiments of the invention have been specifically illustrated and described, it is understood that the invention is not limited thereto, as many variations will be apparent to those skilled in the art, and the invention is to be given its broadest interpretation within the terns of the following claims.

What we claim is:

1. An apparatus for shrinking the heat-shrink film around packaged food products, such as meats, cheeses and the like, which comprises:

a. a frame supporting an oven having enclosing insulated walls which define a tunnel the end walls of which are provided with oppositely spaced openings to provide for the ingress and egress of said packaged food products;

. free swinging curtains attached to each end of said oven so as to cover said openings;

c. support means Within said oven for supporting said packaged food products;

electrical heating means positioned beneath said supporting means, said heating means including in combination therewith control means for maintaining the temperature within said oven at a temperature of at least 212F.

e. a vaporizer pan disposed between said supporting means and said heating means;

f. a water heater including first thermostat means which maintain the temperature of said water within the range of about 190 to 210 F; and

g. a plurality of atomizing noales positioned in said oven above said supporting means, each of said nozzles being operatively connected to said water heater and being capable of producing a full cone of water vapor; whereby said packaged food products in said oven are completely surrounded with a hot wet mist cloud, at a carefully controlled temperature, so as to produce an ideal condition for effecting a shrink rate near the maximum capability of said film and best suited for individual products.

2. The apparatus according to claim 1, wherein said supporting means comprises a flexible, foraminous belt which is movable through said oven, and wherein means are provided for controlling the speed of said belt.

3. The apparatus according to claim 2, wherein said belt comprises a rod conveyor.

4. The apparatus according to claim 1, wherein said oven heating means comprises a plurality of pan heaters and a plurality of air convection heaters, said air convection heaters being positioned beneath said pan heaters.

5. The apparatus according to claim 4, wherein said control means comprises an indicating thermostat having a first pointer which indicates the temperature within said oven and a second pointer which may be set at a desired temperature, said indicating thermostat controlling the operation of a group of said air convection heaters, whereby when said first pointer reaches said second pointer, said indicating thermostat switches off said group of convection heaters connected thereto, causing the temperature in said oven to fall, and after the temperature in said oven has fallen slightly, said indicating thermostat thereupon switches said group of air convection heaters back .on again so that the temperature within said oven will remain very close to the temperature set by said second pointer.

6. The apparatus according to claim 5, wherein said control means includes a percentage input controller connected to a group of air convection heaters, said percentage input controller being adjustable so as to change the percentage of heat output from said group of air convection heaters connected thereto so as to compensate for lower than normal temperatures in said oven which may result from the introduction thereto of a large number of cold products.

7. The apparatus according to claim 6, wherein said pan heaters and said air convection heaters are of U-type configuration and extend transversely of said supporting means.

8. The apparatus according to claim 1, wherein a pressure regulator is associated with said water heater to regulate the pressure of water introduced thereto.

9. The apparatus according to claim 8, wherein a solenoid valve is associated with said water heater to control the flow of water therefrom to said atomizing nozzles, said solenoid valve being 0 n when said water heater is on.

l e apparatus according to claim 1, wherein said shrink tunnel is equipped with a temperature warning light controlled by a thermostat located at the discharge end of said tunnel, said thermostat being pre-set for a temperature which should not be exceeded, whereby said warning light will come on when the temperature within said oven exceeds said pre-set temperature.

11. The apparatus according to claim 1, including a high temperature safety electrical disconnect system which automatically shuts down said apparatus when it is overheated. 

1. An apparatus for shrinking the heat-shrink film around packaged food products, such as meats, cheeses and the like, which comprises: a. a frame supporting an oven having enclosing insulated walls which define a tunnel the end walls of which are provided with oppositely spaced openings to provide for the ingress and egress of said packaged food products; b. free swinging curtains attached to each end of said oven so as to cover said openings; c. support means within said oven for supporting said packaged food products; d. electrical heating means positioned beneath said supporting means, said heating means including in combination therewith control means for maintaining the temperature within said oven at a temperature of at least 212*F. e. a vaporizer pan disposed between said supporting means and said heating means; f. a water heater including first thermostat means which maintain the temperature of said water within the range of about 190* to 210* F; and g. a plurality of atomizing nozzles positioned in said oven above said supporting means, each of said nozzles being operatively connected to said water heater and being capable of producing a full cone of water vapor; whereby said packaged food products in said oven are completely surrounded with a hot wet mist cloud, at a carefully controlled temperature, so as to produce an ideal condition for effecting a shrink rate near the maximum capability of said film and best suited for individual products.
 2. The apparatus according to claim 1, wherein said supporting means comprises a flexible, foraminous belt which is movable through said oven, and wherein means are provided for controlling the speed of said belt.
 3. The apparatus according to claim 2, wherein said belt comprises a rOd conveyor.
 4. The apparatus according to claim 1, wherein said oven heating means comprises a plurality of pan heaters and a plurality of air convection heaters, said air convection heaters being positioned beneath said pan heaters.
 5. The apparatus according to claim 4, wherein said control means comprises an indicating thermostat having a first pointer which indicates the temperature within said oven and a second pointer which may be set at a desired temperature, said indicating thermostat controlling the operation of a group of said air convection heaters, whereby when said first pointer reaches said second pointer, said indicating thermostat switches off said group of convection heaters connected thereto, causing the temperature in said oven to fall, and after the temperature in said oven has fallen slightly, said indicating thermostat thereupon switches said group of air convection heaters back on again so that the temperature within said oven will remain very close to the temperature set by said second pointer.
 6. The apparatus according to claim 5, wherein said control means includes a percentage input controller connected to a group of air convection heaters, said percentage input controller being adjustable so as to change the percentage of heat output from said group of air convection heaters connected thereto so as to compensate for lower than normal temperatures in said oven which may result from the introduction thereto of a large number of cold products.
 7. The apparatus according to claim 6, wherein said pan heaters and said air convection heaters are of U-type configuration and extend transversely of said supporting means.
 8. The apparatus according to claim 1, wherein a pressure regulator is associated with said water heater to regulate the pressure of water introduced thereto.
 9. The apparatus according to claim 8, wherein a solenoid valve is associated with said water heater to control the flow of water therefrom to said atomizing nozzles, said solenoid valve being open when said water heater is on.
 10. The apparatus according to claim 1, wherein said shrink tunnel is equipped with a temperature warning light controlled by a thermostat located at the discharge end of said tunnel, said thermostat being pre-set for a temperature which should not be exceeded, whereby said warning light will come on when the temperature within said oven exceeds said pre-set temperature.
 11. The apparatus according to claim 1, including a high temperature safety electrical disconnect system which automatically shuts down said apparatus when it is overheated. 